Can you build a duplex on your block?

Short answer: We do not guess. Plenty of builders will stand on a block and tell you what fits before anyone has looked at anything, and that answer is worth what you paid for it. On our jobs the question goes to the people qualified to answer it. An architect looks at whether the land sits in a bushfire area, whether it carries special conditions, and whether required offsets change what can actually be built there. A stormwater engineer looks at flooding, which changes how the whole site gets built and can either add a lot of cost or limit what goes on the block at all. A surveyor, a geotechnical engineer, a town planner and a structural engineer each look at their own part of it. Only then does anyone tell you what your block can take.

Why we will not answer it on the spot

The honest reason is that the answer is not ours to give. Whether a duplex fits your block depends on planning controls, on what is registered against the title, and on physical conditions nobody can see from the footpath.

A builder who answers that question standing in your driveway is guessing. They might be guessing well, from experience. It is still a guess, and you are the one who wears it if it turns out wrong after you have bought the land.

So the first thing that happens is not an opinion. It is a set of people looking at your specific block.

Who actually looks at it

There are six disciplines involved before we will price a duplex build:

• Surveyor
• Architect
• Geotechnical engineer
• Town planner
• Structural engineer
• Stormwater engineer

How many of them you need depends on what information already exists. A lot of it comes out of the contract of sale, and if the site has already been through DA or CDC approval, a good deal of the work has been done and documented. If it has not, there is more to find out.

What they find

Two of them tend to change the answer most, so those are worth explaining.

The architect looks at whether the land is in a bushfire area, whether it carries special conditions, and whether there are offsets that change the design. That last one matters more than people expect. Required offsets can change what the customer actually wants and what ends up getting delivered, which is a very different conversation to have before you buy than after.

The stormwater engineer looks for flood-related issues. If the site has them, it changes the plan for how the whole site gets built. That can cost a lot extra, and in some cases it limits what can be constructed on the block at all.

The others cover the ground you would expect them to. We are not going to put words in their mouths, because each of them signs off on their own work.

What changes the cost

Separate from whether it can be built, there are things that change what it costs to build. We look at all of these at the start rather than discovering them later.

Falls on the land. How much the block drops, and which side it drops towards. Front and back are not the same problem.

Easements. Something registered on the title giving someone else rights over part of your land. It affects where a building can sit.

Sewer. Where the line runs, and what has to happen if it runs where you want to build.

Flooding, as above.

None of these mean a block is unbuildable. They mean the number changes, and they are much cheaper to know about before you own the land than after. If you want an indicative figure for your own situation while you are working through this, the build cost calculator takes about two minutes.

Who pays for all this

Straight answer: you do, and you pay them directly.

The architect and the other consultants are engaged in your name, not ours. Their contracts are yours, their reports are yours, and you pay them as they come along. That is not us pushing costs onto you. It is how it should work, because their advice is yours to keep and to use with whoever ends up building.

Our contract is the build contract, and it starts at roughly demo or construction. Everything before that point is us helping you get there.

We would rather say that plainly than dress it up. Six disciplines is real money, and you should know it going in rather than find out at signing.

What we do before the contract starts

Most of the time, if you come to us at the start, we work through it with you step by step. Reading what you already have, telling you what still needs finding out, and being straight about what looks difficult. That does not cost you anything, because our contract has not started yet.

Here is what that looked like on one job.

Someone came to us who had already bought their block. They wanted to build a co-living home on it. We did the early work with them at no charge, and it turned out the site was flood affected.

On that site, that meant the faster approval path was off the table. It would have had to go through a full development application instead, which meant more time and more money than they had planned for. They decided not to go ahead.

That was the right call and it was their call to make. It was also an expensive way to find out, because most of the cost was already locked in the day they bought the land. Had we been in that conversation a few months earlier, the same finding would have cost them a phone call.

Come to us before you buy, not after

Most of the time we will help someone who is still looking at a site. It is a much better conversation at that stage, because everything is still a choice.

Once you own the block, the constraints are yours. Before you own it, they are information. That is the whole difference, and it is why we would rather hear from you early.

When something on a site does look difficult, we sit down with you one on one and put the details, the risks and the problems in front of you. Then it is your call whether to go ahead or walk away. We are not going to make that decision for you, and we are not going to talk you past a problem you should know about.

If you are weighing up the approval side as well, we covered that separately in CDC versus DA. And if you are looking at a co-living build rather than a duplex, what makes a block right for co-living covers the same ground for that product.

Common questions

Can you tell me if a duplex fits my block?
Not from a photo or an address, no. The answer depends on planning controls, what is registered against the title and physical site conditions, and those get assessed by an architect, a town planner and the other consultants rather than by us. What we can do is look at what you have, tell you what still needs finding out, and be honest about what looks difficult.

What usually stops a duplex going ahead?
The two that change the answer most in our experience are a bushfire area or special conditions on the land, which the architect picks up, and flooding, which the stormwater engineer picks up. Flooding in particular can change how the whole site has to be built, add significant cost, or limit what can go on the block.

Do I have to pay for all six consultants?
You pay them, and you pay them directly, because their contracts are in your name rather than ours. Not every project needs all six, and how much each does depends on what already exists. Our own contract is the build contract and it starts at around demo or construction, so the work we do with you before that does not cost you anything.

Should I talk to a builder before I buy the land?
We think so. Most of the time we will help someone who is still looking at a site, and it is a far more useful conversation before you own it. After settlement the constraints are yours to deal with. Before settlement they are just information you can act on.